Success in cancer therapy has conventionally been accomplished by surgical reduction of a tumor mass and subsequent chemo- and/or radiotherapy. This strategy can reduce the tumor and, in less advanced stages, often results in complete remission. Unfortunately, the prognosis for more advanced tumors has changed little over the past 50 years and a significant proportion of cancer-related deaths are caused by subsequent metastases. New prophylactic and therapeutic treatments are needed to combat the increasing occurrence of cancer.